Etymology Coined, theo- + -ism. ultimately from Ancient Greek θεός (theós, “god”). Attested in English from 1678, theist being attested 16 years earlier in 1662. Cognate French théisme, as in Diderot Principes de la philosophie morale (1745), which was probably borrowed from English.
1
Belief in the existence of at least one deity.
2
Belief in the existence of a personal creator god, goddess, gods and/or goddesses present and active in the governance and organization of the world and the universe. The God may be known by or through revelation.
The term stands in contradistinction to theism which, in its widest sense, means belief in a personal god, goddess, gods and/or goddesses.1999, Jeaneane D. Fowler, Humanism: Beliefs & Practices, page 66
Etymology Borrowing from New Latin thea (“tea”, noun) + English -ism.
1
Medicine, Pathology, Sciences A morbid condition resulting from excessive consumption of tea.
"Theism" belongs to that genus of disease in which morphinism, caffeinism, and vanillaism belong.1888, John C. Cutter, “Narcotics, stimulants, and depressants”, in Comprehensive anatomy, physiology, and hygiene : adapted for schools, academies, colleges, and families : with instruction on the effects of stimulants and narcotics, and brief directions for illustrative dissections of mammals, for elementary work with the microscope, for physiological demonstrations on the human body, and for the management of emergent cases, 3rd edition, Philadelphia: J. B. Lippincott, →OCLC, page 350:
A single cup of tea may cause excitement and insomnia, while a stronger dose rarely fails to produce acute "theism," characterized by excitement, hyperaesthesia, palpitation, sweats, and frequent micturition; it may occasionally simulate delirium tremens, […]1906 September 15, “Our breakfast beverages”, in The British Medical Journal, volume 2, London: British Medical Association, →ISSN, page 653: